1. Field of the Invention
This invention relates to a method of finishing slide fastener stringers of continuous length or "fastener chains" having a continuous plastic filament spirally formed and secured to an edge of a stringer tape during the weaving or knitting thereof.
2. Prior Art
There have been proposed a number of slide fasteners or zippers of the type described, which comprise a woven or knitted stringer tape and a coupling fastener element made of a plastic filament anchored into a longitudinal edge of the tape, the filament being usually formed into a helical coil structure consisting of a row of successive elongated loops or convolutions each having a coupling head, an upper and a lower leg and a connecting portion.
When the filament is formed into a row of helically coiled coupling loops and mounted on a stringer tape, such loops would usually present a cross-sectionally oval shape which is not complimentary with the inner guide surfaces of a slider and hence would often interfere with the sliding movement of the latter during opening and closing of the fastener stringers. With a view to eliminating this difficulty, it has been proposed to cover the coupling loops with covering threads over their upper and lower surfaces including their heel portions in such a manner that the covered portions of the loops present a transverse cross section complimentary in shape with the guide channel of the slider. Tape thread systems woven or knitted are susceptible to deformation as they tend to expand or contract upon weaving or knitting of the tape. The rows of fastener elements (coupling loops) mounted on such dimensionally unstable tape would of necessity become shifted out of position relative to each other and displaced or separated from the tape. Furthermore, the covering threads disposed over the fastener elements are rather soft and bulky in nature which in turn creates an increase in the resistance of the covering threads to sliding movement of the slider, resulting in disagreeable, sometimes interrupted coupling or uncoupling engagement of the cooperating stringers.